1. Field of the Invention
The present invention relates generally to a light transmission system for medical treatment, such as photodynamic therapy, in combination with a photoactive drug.
2. Description of the Related Art
In photodynamic therapy (PDT), light of a specific wavelength or waveband is directed toward a target cell or cells that have been rendered photosensitive through the administration of a photoreactive, photoinitiating, or photosensitizing agent. This photoreactive agent has one or more characteristic light absorption wavelengths of which at least one has a large peak. The large peaks occur at “excitation wavelengths” that may be useful in PDT. The drug is commonly administered to a patient via intravenous injection, oral administration, or by local delivery to the treatment site. Once the photoactive agent has associated itself with abnormal cells, the abnormal cells can be treated by exposure to an appropriate excitation wavelength of the photoreactive agent.
The objective of PDT may be either diagnostic or therapeutic. In diagnostic applications, the wavelength of light is selected to cause the photoreactive agent to fluoresce as a means to acquire information about the targeted cells without damaging the targeted cells. In therapeutic applications, the wavelength of light delivered to the targeted cells treated with the photoreactive agent causes the agent to undergo a photochemical reaction with oxygen in the targeted cells to yield free radical species (such as singlet oxygen), which in turn cause any or all of cell lysis, cell necrosis, and occlusion of (new) blood vessels.
One type of light delivery system used for PDT treatments comprises the delivery of light from a light source, such as a laser, to the targeted cells using an optical fiber delivery system with special light-diffusing tips on the fibers. This type of light delivery system may further include optical fiber cylindrical diffusers, spherical diffusers, micro-lensing systems, an over-the-wire cylindrical diffusing multi-optical fiber catheter, and a light-diffusing optical fiber guide wire. This light delivery system generally employs a remotely disposed high-powered laser, or solid state laser diode array, coupled to optical fibers for delivery of the light to the targeted cells.
The light source for the light delivery system used for PDT treatments may also be light emitting diodes (LEDs). LEDs may be arrayed in an elongate device to form a “light bar” for the excitation light delivery system. The LEDs may be either wire bonded or electrically coupled utilizing a “flip chip” technique that is used in arranging other types of semiconductor chips on a conductive substrate. Various arrangements and configurations of LEDs are described in U.S. Pat. Nos. 6,958,498; 6,784,460; and 6,445,011.
Several devices shown in the literature are intended for use in photodynamic therapy and generate light inside the body, once inserted. For example, U.S. Pat. No. 5,445,608 depicts a flexible array of light transmitters that are inserted transcutaneously. These devices are reusable, generally, and have features while apparently offering cost reduction, also poses risks: infection due to improper sterilization, and improper treatment due to potential undetected failure of some of the reused light transmitters in the arrays. In addition, in reuse of most equipment, there are additional parts and labor costs in servicing and maintaining the equipment.
One of the challenges in design and production of light bars relates to size: large diameter light bars cause significant trauma to tissue through which it passes, and have potentially painful effects for the patient. However, light bar size is dictated by several factors including the size of light emitters that emit light of wavelength desired at a sufficient energy level, and the fragility of the bar as its thickness is reduced which increases risk of breaking in the patient. Accordingly, there is a need for smaller high powered LEDs, thinner light bars that are not too fragile for safe use for their intended purpose, and a device that is single use after removal from a sterile pack, and conveniently supplied with an appropriate amount of a photoactive agent.